Process for dispersing or redispersing a Group VIII noble metal species on a porous inorganic support

ABSTRACT

A process for dispersing or dispersing relatively large crystallites of an agglomerated Group VIII noble metal species present on a porous inorganic support is disclosed. The process includes contacting the agglomerated noble metal species, e.g., palladium or platinum, present on the support, e.g., alumina, silica or a zeolite such as ZSM-5 from which at least a major portion of any extraneous matter such as coke or other residue has previously been removed, with nitric oxide (NO) alone or in admixture with a source of halogen such as Cl 2  and thereafter removing sorbed nitrogen oxide(s) and halogen, if present. The thus treated metal-loaded catalyst demonstrates substantially increased benzene hydrogenation activity (BHA) compared to the same catalyst prior to treatment indicating significant dispersion/redispersion of the metal crystallites as smaller crystallites.

This is a continuation of copending application Ser. No. 089,654, filedon Aug. 26, 1987, now U.S. Pat. No. 4,849,385.

BACKGROUND OF THE INVENTION

This invention relates to a process for dispersing or redispersing acatalytically active noble metal species on a porous inorganic supportwhich itself may or may not possess catalytic activity, e.g., dispersingor redispersing palladium or platinum on a zeolite catalyst such asZSM-5 which has become deactivated due to the accumulation ofcarbonaceous material (e.g., coke) during the course of its use in ahydrocarbon conversion operation such as catalytic dewaxing.

Heterogeneous porous inorganic acidic oxides are used extensively in thepetroleum and petrochemicals industry to catalyze a variety ofhydrocarbon conversions. These conversions include catalytic cracking,hydrocracking, naptha reforming, benzene alkylation, xyleneisomerization, catalytic dewaxing, and other conversions.

During use, as is generally know, the catalysts undergo progressive lossof catalytic activity and/or selectivity. The time required for theactivity to decay to the point at which the catalyst is no longer usefulmay vary from as little as a few minutes, as in catalytic cracking, toseveral years, as with some versions of naptha reforming. Some of thefactors which affect the aging rate include the nature of the feed, thenature of the catalyst and process conditions. In general, catalystdeactivation is accompanied by an accumulation of carbonaceous matter onthe catalyst, and is was early learned to regenerate deactivatedcatalysts by burning the carbonaceous matter in an oxygen-containinggas. In the case of metal-loaded catalysts, the severity of the burningoperation often leads to agglomeration of the metal component intorelatively large crystallites which, of course, are inherently lessactive than small crystallites which possess a greater surface area foran equivalent amount of metal.

Reactivation of noble metal catalysts utilized in hydrocarbon processingprocedures such as reforming is known in the art. Processes whichutilize chlorine and oxygen in catalyst reactivation are well known. Forexample, U.S. Pat. No. 2,906,702 disclosed a method of restoring theactivity of an alumina-supported platinum catalyst after deactivationoccurring during the reforming of hydrocarbons. According to thismethod, a deactivated platinum-alumina catalyst is contacted withgaseous chlorine, fluorine, or other halogen or halogen-affordingsubstance at an elevated temperature.

U.S. Pat. No. 3,134,732 describes a method for reactivating noble metalcatalyst supported on alumina by contacting the catalyst withhalogen-containing gas, stripping excess halogen therefrom andsubjecting the resulting catalyst to a reduction step with ahydrogen-containing gas. This treatment is intended to break up thelarge noble metal crystallites into smaller crystallites.

U.S. Pat. No. 3,201,355 discloses reactivating a deactivated metaloxide-supported noble metal catalyst utilized in hydroforming processes.Reactivation is accomplished under anhydrous conditions employing agaseous source of halogen such as chlorine (which is preferred) ornitrosyl chloride admixed with an oxygen-containing gas such as air oran inert gas such as nitrogen or carbon dioxide as the reactivatingagent.

U.S. Pat. No. 3,625,860 discloses a process for activating and/orreactivating a platinum on alumina reforming catalyst by contacting thecatalyst which has been previously subjected to a sequence of oxidativeburn-off, oxygen treatment, purging and reducing operations with anonmetallic chloride-containing compound, e.g., an organic chloride suchas tertiary butyl chloride, propylene dichloride, carbon tetrachloride,etc., or an inorganic chloride such as hydrogen chloride.

It is also known in the art to regenerate platinum groupmetal-containing zeolite catalysts. Regeneration of noble metal-loadedzeolite catalysts requires certain procedural modifications because themetal must be returned in a dispersed form within the zeolite pores.

U.S. Pat. No. 3,986,982 describes a procedure in which deactivatedplatinum group metal-loaded zeolite is contacted with a stream of inertgas containing from 0.5 to 20 percent volume of free oxygen and from 5to 500 ppm volume of chloride as chlorine, HCl, or an organicchlorine-containing material. The resulting catalyst is purged to removeresidual oxygen and chlorine and then reduced in a stream of hydrogen at200° to 600° C.

Other processes for regenerating or otherwise treating metal-loadedzeolites, most of which feature the use of molecular chlorine or othersource of chlorine, are described in U.S. Pat. Nos. 3,943,052;4,444,895; 4,444,897; 4,447,551; 4,517,076; 4,518,708; 4,600,700;4,645,751; and, commonly assigned copending U.S. patent application Ser.No. 819,074, filed Jan. 15, 1986; U.K. patent application No. 2,106,413and European patent application No. 142,352.

Processes for treating catalysts featuring the use of an oxide ofnitrogen are also known.

U.S. Pat. No. 3,243,383 discloses a process for regenerating a spentcobalt oxide on carbon catalyst, useful in olefin polymerization,wherein the spent catalyst, following heating at 250°-1000° C. in aninert atmosphere and cooling, is treated with nitric acid, nitric oxide(NO), nitrogen dioxide gas (NO₂) or mixtures thereof and thereafterammoniated, if desired, and finally heated to reactivation temperature.

U.S. Pat. No. 3,451,942 describes a process for the rejuvenation of adeactivated hydrocracking catalyst containing ahydrogenation-dehydrogenation component present in the form of largecrystallites on an acidic cracking component, e.g., anarsenided-nickel-on-fluorided-silica-alumina catalyst, in which thedeactivated catalyst, following removal of at least a major part of theaccumulated carbonaceous matter therefrom, is treated with a nitrogenoxide selected from the group consisting of NO, NO₂, N₂ O and N₂ O₃,optionally, in aqueous nitric acid solution, under conditions causingthe material to react with the hydrogenation-dehydrogenation component.Thereafter, the catalyst is treated with oxygen which reacts with thehydrogenation-dehydrogenation component followed by reduction of thelatter with hydrogen. It is hypothesized that thehydrogenation-dehydrogenation component is sequentially converted inthis series of operations to a salt, possibly a nitrate, then, followingthe treatment with oxygen, into an ionic form and finally, followingreduction with hydrogen, into small crystallites.

According to the process for regenerating a supported tellurium and/ortellurium compound-containing catalyst disclosed in U.S. Pat. No.3,536,631, the deactivated catalyst is treated at 50°-400° C. with agaseous nitrogen oxide of the formula NO_(x) in which x is 1, 1.5, 2 or2.5 and/or a gaseous oxyacid of nitrogen of the formula HNO_(y) in whichy is 2 or 3.

Deactivated phosphomolybdic acid based catalysts which are used for theconversion of saturated and unsaturated aldehydes to acids arereactivated by the process of U.S. Pat. No. 4,471,062 by feeding anoxide of nitrogen, preferably nitric oxide (NO), over the deactivatedcatalyst at 100°-400° C.

Che et al., "A Study of the Chemisorption of Nitric Oxide on PdYZeolite. Evidence For a Room Temperature Oxidative Dissolution of PdCrystallites", J. Phys. Chem. 80, 2371-2381 (1976) describes theredispersion of mildly agglomerated palladium, i.e., crystallites of 20Angstroms, supported on zeolite Y with nitric oxide at room temperature.It has been observed that in the case where agglomerated noble metalcrystallites of at least about 25 Angstroms average diameter, and moreusually at least about 100 Angstroms average diameter, are concerned,e.g., a crystallite size which is typical of a supported noble metalcatalyst which has experienced a coke burn-off operation, theredispersion procedure described in this publication does not provideconsistent results unless a nitric oxide(s) stripping operation (ofwhich no mention is made by Che et al.) is carried out at the conclusionof the nitric acidcontacting operation.

Foger et al., "The Redispersion of Iridium on SiO₂ and Gamma-Al₂ O₃Supports with Chlorine-containing Gases", J. Catalysis, 96, 154-169(1985) discloses that while a gaseous mixture containing a major amountof chlorine and a minor amount of nitric oxide is effective forredispersing iridium on alumina, the mixture is not effective forredispersing iridium on silica. Similarly, Foger et al., "Redispersionof Pt-Ir Supported on Gamma-Al₂ O₃ and SiO₂ in Chlorine-ContainingGases" discloses that the aforesaid chlorine-nitric oxide mixture is noteffective for redispersing bimetallic Pt-Ir on silica. There is nosuggestion in either of these publications of what the effect of using achlorine-nitric oxide mixture in which the nitric oxide isquantitatively the major reactant would be.

SUMMARY OF THE INVENTION

In accordance with the present invention, a process is provided fordispersing or redispersing a Group VIII noble metal species present on aporous inorganic support which comprises:

(a) contacting a supported Group VIII noble metal species possessing anaverage crystallite diameter of at least about 25 Angstroms with nitricoxide at a temperature providing dispersion or redispersion of the noblemetal species on the support, the support being a porous inorganicmaterial from which at least a major amount of any carbonaceous matterwhich may have been present thereon has been removed prior to contactingwith nitric oxide

(b) removing sorbed nitrogen oxide(s) from the supporteddispersed/redispersed noble metal species.

The process of this invention can be used to initially disperse thenoble metal species when preparing the fresh catalyst as well as toredisperse the agglomerated noble metal species component of a"deactivated catalyst", i.e., a catalyst of diminished activity comparedto that of the freshly prepared catalyst, resulting from the use of thecatalyst in a chemical conversion process. Dispersion or redispersioneffects a reduction in the average diameter, or size, of the noble metalcrystallites. For example, when applied to a supported noble metalspecies possessing an initial average crystallite size of from abut 100to about 1000 Angstroms, i.e., a relatively highly agglomerated metalcomponent, the process of this invention can readily provide adispersed/redispersed metal species whose average crystallite size hasbeen reduced by a factor of up to 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The dispersion/redispersion process of this invention is carried outupon a supported Group VIII noble metal species, e.g., a metal such asplatinum, palladium, iridium, osmium, rhodium or ruthenium. The noblemetal species may be present in elemental form or as a compound, e.g.,as an oxide or sulfide. Alloys of two or more noble metal species arecontemplated. The noble metal species can also be associated with anon-noble metal component present as a promoter. The latter can beselected from the group consisting of Group IB, Group IVB, Group VIIA,and non-noble Group VIII metals. Generally, the catalyst treated by thepresent invention possesses a noble metal content ranging from about0.01 to about 10, and preferably about 0.1 to about 3, weight percent.

The porous inorganic support can be any of those encountered in thecatalyst art and include materials such as alumina and silica and otherhighly siliceous materials, both of the amorphous and crystallinevariety. Included among the latter are the crystalline aluminosilicates(inclusive of related materials in which aluminum is replaced in wholeor in part with one or more other trivalent elements), or zeolites,which may or may not be composited with one or more inorganiccatalytically active or inactive refractory binders.

The zeolites constitute an especially prominent class of catalyticallyactive support which are suitable for the practice of this invention.Included among the useful zeolites are zeolite A (U.S. Pat. No.2,882,243), zeolite X (U.S. Pat. No. 2,882,244), zeolite Y (U.S. Pat.No. 3,130,007), zeolite ZK-5 (U.S. Pat. No. 3,247,195), zeolite beta(U.S. Pat. No. 3,308,069; Re. 28,341), zeolite XK-4 (U.S. Pat. No.3,314,752), zeolite ZSM-5 (U.S. Pat. No. 3,702,886; Re. 29,948), zeoliteZSM-11 (U.S. Pat. No. 3,709,979), zeolite ZSM-12 (U.S. Pat. No.3,832,449), zeolite ZSM-20 (U.S. Pat. No. 3,972,983), ZSM-35 (U.S. Pat.No. 3,016,245), ZSM-38 (U.S. Pat. No. 4,046,859) and zeolite ZSM-23(U.S. Pat. No. 4,076,842), merely to name a few.

When, in accordance with the process of this invention, it has becomeapparent that the supported noble metal catalyst composition has becomedeactivated, e.g., as a result of its use in a hydrocarbon processingoperation, the operation is terminated by discontinuing the flow offeedstock to the reactor. It is preferred that the reactor be purged offeedstock by feeding a gaseous reducing agent, preferably dry hydrogen,therethrough. It is contemplated that temperatures of from about 250° C.to about 550° C. and pressures ranging from atmospheric to the operatingpressure of the process, e.g., up to about 70 atmospheres, can be usedin this operation. Purging the reactor with hydrogen under theseconditions simultaneously effects stripping of the catalyst andreduction of any oxidized metal component thereon to the zerovalentstate. Of course, reduction of oxidized metal component can beaccomplished apart from any purging of the reactor. The reactor can alsobe purged subsequently with an inert gas in order to remove thehydrogen. Suitable purge conditions include temperatures of from about25° to about 450° C. and pressures of about 1 to 40 atm, using a streamof an inert gas such as nitrogen.

The catalyst is then treated in an oxidizing atmosphere in order to burnoff at least a major amount of any carbonaceous deposits which may bepresent, e.g., coke as well as nitrogen or sulfur compounds. Thisburning operation is not narrowly critical and suitable conditions rangefrom temperatures of about 260° to about 538° C. (500° to 1000° F.) oreven higher and oxygen concentrations range from about 0.10 to 10 molpercent. The duration of the coke burning step is also not narrowlycritical and will obviously vary depending on the temperature, oxygenconcentration and the amount of coke on the catalyst. Preferredoperation of the coke burning step includes treating a spent catalystwith about 0.2 to 7 mol percent of oxygen at temperatures of about 370°to about 454° C. (700° to 850° F.) and pressures of from about 1 to 70atmospheres. Where the support component of the catalyst is a zeolite,it is preferable that the burn-off conditions be not so severe as tocause any substantial loss in zeolite crystallinity. At this point, anyremaining carbon dioxide can be purged from the reactor with an inertgas such as helium or nitrogen.

Following any coke burn-off operation, the metal-loaded catalyst iscontacted with gaseous nitric oxide (NO), optionally, in combinationwith a relatively minor amount of a source of gaseous halogen,preferably, chlorine gas. An inert diluent such as helium or nitrogencan also be present. The conditions of this operation can vary widelyand include a concentration of nitric oxide of at least about 0.1 volumepercent, preferably at least about 1 volume percent and still morepreferably at least about 10 volume percent, a concentration of gaseoushalogen or source of halogen where utilized of from about 0.01 to about0.1 volume percent, preferably from about 0.05 to about 5 volume percentand still more preferably from about 0.2 to about 2 percent and aconcentration of inert diluent gas, e.g., nitrogen, where utilizedrepresenting the balance of the nitric oxide-containing atmosphere. Thelatter can be introduced to the contacting zone maintained at atemperature of from about 0° F. to about 1000° F., preferably at fromabout 40° to about 800° F. and still more preferably at from about 200°to about 750° F., a pressure ranging from atmospheric to about 100atmospheres, preferably from about 0.5 to about 50 atmospheres and stillmore preferably from about 1 to about 10 atmospheres at a volumetricflow rate of from about 100 to about 15,000 gaseous hourly spacevelocity (GHSV), preferably at from about 200 to about 10000 GHSV andstill more preferably at from about 600 to about 6000 GHSV. In general,contact times of from about 10 minutes to 24 hours or more, preferablyfrom 30 minutes to 20 hours and still more preferably from about 1 toabout 16 hours provide entirely acceptable results.

Following contact with NO and prior to its use as a catalyst, thesupported, dispersed/redispersed noble metal species is purged of sorbedNO_(x) wherein x is 0.5 to 2. This can be readily accomplished bysweeping the catalyst composition with a suitable gaseous purge medium,helium being advantageously employed for this purpose The purgeoperation will normally be carried out under conditions effecting theremoval of at least a substantial part, and preferably essentially all,of such sorbed nitrogen oxide(s). Helium purge conducted at elevatedtemperature, e.g., from about 200° to about 1000° F. and preferably from500° to about 900° F. for from 10 minutes to 10 hours or more, andpreferably from about 30 minutes to about 2 hours generally providesgood results.

The following examples are illustrative of the process fordispersing/redispersing metal on a porous inorganic acidic catalyst inaccordance with the present invention. In all examples, the treatedcatalysts were purged with helium at 850° F. for 1 hour.

EXAMPLE 1

A metal-loaded catalyst comprising 0.4 weight percent palladium on abound ZSM-5 catalyst containing 65 weight percent ZSM-5 and 35 weightpercent alumina (Catalyst A) was prepared. The properties of thiscatalyst are set forth in Table 1 as follows:

                  TABLE 1                                                         ______________________________________                                        Properties of Fresh Catalyst A                                                ______________________________________                                        Palladium, weight percent                                                                         0.35                                                      Sodium, weight percent                                                                            0.027                                                     Chlorine, weight percent                                                                          0.21                                                      Density, g/cc                                                                 Packed              0.543                                                     Particle            0.890                                                     Real                2.611                                                     Pore Volume, cc/g   0.741                                                     Surface Area, M.sup.2 /g                                                                          339                                                       ______________________________________                                    

A portion of Catalyst A was deactivated in an atmosphere of 80 volumepercent hydrogen and 20 volume percent steam at 840° F. and 1 atm for 1hour and purged with helium at. the same temperature for 0.5 hour(Catalyst B).

Another portion of Catalyst A was used in hydrodewaxing 650°F.+petroleum chargestocks at conditions of 400 psig H₂, 1 LHSV, 2500 scfH₂ /bbl, 540° F. start-of-cycle temperature and 675° F. end-of-cycletemperature. The duration of this test was 63 days after which the cokedcatalyst was removed from the reactor. A sample of the coked catalystwas hydrogen reactivated at 900° F. for 18 hours and oxygen regenerated,both operations being carried out at atmospheric pressure, in a glassreactor from about 750° F. to a maximum temperature of 850° F. inincreasing oxygen concentration. Elemental analyses of the coked,reactivated, and regenerated catalyst (Catalyst C) are shown in Table 2as follows:

                  TABLE 2                                                         ______________________________________                                        Elemental Analysis of Catalyst C                                              Element, %                                                                              Coked    H.sub.2 Reactivated                                                                        O.sub.2 Regenerated                           ______________________________________                                        Carbon    7.95     3.54         0.015                                         Nitrogen  0.20     0.21         <0.03                                         Sulfur    0.10     0.03         0.04                                          Sodium     0.023    0.026       0.01                                          Palladium 0.34     0.38         0.43                                          Iron       0.077    0.075       0.097                                         ______________________________________                                    

Another portion of the coked catalyst was regenerated at 100 psig, 850°F. maximum temperature, 7% maximum oxygen concentration and in thepresence of 70 torr water vapor. Analysis of the regenerated catalyst(Catalyst D) by scanning scanning transmission electron microscopic(STEM) analysis showed the average size of the agglomerated palladiumcrystallites to be about 100 Angstroms or larger.

In still another example, a commercial 0.5% Pd/Al₂ O₃ catalyst wasdeactivated in an atmosphere of 80% hydrogen and 20% steam at 840° F.for 1 hour (Catalyst E).

Catalysts B-E were contacted with 75 volume percent NO and 25 volumepercent hydrogen or helium under varying conditions of temperature andtime. The redispersion of palladium on Catalysts B-E was monitored bybenzene hydrogenation activity (BHA) and STEM analysis. Thehydrogenation of benzene to cyclohexane is commonly used to determinecatalytic activity of noble metal catalysts. The reaction is generallyobserved as structure insensitive which means that the specific metalactivity is not a function of the size geometry, and orientation of themetal particles on the catalyst. Hence, the test can be used as ameasure of the overall extent of metal dispersion.

In this test, a gaseous mixture containing 100:1 molar ratio of hydrogenand benzene is passed through a vertical vycor tubular reactor, 1/4" IDand 5" long containing about 250 mg of the palladium catalyst at ahydrogen flow rate of 200 cc/min and a total pressure of 1 atm. Thetemperature range is from 73°-300° F. depending on the activity of thecatalyst. Before the introduction of benzene, the catalyst is reduced inflowing hydrogen from ambient temperature to a final temperature of 400°F.

The benzene hydrogenation activity of fresh, deactivated, and nitricoxide rejuvenated catalysts are shown in Table 3 below. In all cases,the rejuvenated catalyst samples have higher activity than thedeactivated samples.

                  TABLE 3                                                         ______________________________________                                        Benzene Hydrogenation Activity of Palladium                                   Catalysts (Mole/mole Pd/hr at 212° F.)                                 Catalyst   BHA        NO Treatment                                                                              BHA                                         ______________________________________                                        A (Control)                                                                              24.6                                                               B          3.2        400° F., 2.5 hr                                                                    28.8                                        C          15.7       400° F., 2.5 hr                                                                    19.9                                        D          0.2        400° F., 2.5 hr                                                                     7.1                                                              750° F., 3.0 hr                                                                    24.5                                        E          0.2        400° F., 2.4 hr                                                                    23.5                                        ______________________________________                                    

EXAMPLE 2

In place of contacting deactivated Catalysts B-D with NO alone as inExample 1, the catalysts were contacted with a gaseous mixture of 50volume percent NO, 2 volume percent Cl₂ and 48 volume percent N₂(diluent) at 390° F. and a total flow of 100 cc/min for 2.5 hrs.

The extent of redispersion as measured by the BHA test is set forth inTable 4 as follows:

                  TABLE 4                                                         ______________________________________                                        Benzene Hydrogenation Activity (Mole/mole                                     Pd/hr at 212° F.)                                                                   Benzene                                                                       Hydrogenation Activity                                                          Before    After                                                Catalyst       Treatment Treatment                                            ______________________________________                                        A (Control)    24.6      --                                                   B              3.2       64.7                                                 C              15.7      49.6                                                 D              0.2       39.1                                                 ______________________________________                                    

It may be noted that the BHA, and therefore the extent of palladiumdispersion, of the deactivated catalysts exceeded that of the freshlyprepared catalyst.

EXAMPLE 3

This example compares the effectiveness of NO for redispersing palladiumon ZSM-5 with that of NO₂.

The conditions of treating regenerated Pd ZSM-5 catalysts with NO, NO₂or NO/Cl₂ and the BHA levels (mole/mole Pd/hr) of the treated catalystsare set forth in the following table.

                  TABLE 5                                                         ______________________________________                                        Comparison of NO with NO.sub.2 For The                                        Redispersion of Pd on ZSM-5                                                                     Benzene Hydrogenation                                                         Activity (at 212° F.)                                           Treatment    Before    After                                       Catalyst   Conditions   Treatment Treatment                                   ______________________________________                                        Catalyst C NO.sub.2 at 400° F. for                                                             15.7      11.8                                        (from Example 1)                                                                         2.5 hours                                                          Catalyst C NO at 400° F. for                                                                   15.7      19.9                                                   2.5 hours                                                          Catalyst D NO.sub.2 at 400° F. for                                                             0.2       6.1                                         (from Example 1)                                                                         2.5 hours                                                          Catalyst D NO at 400° F. for                                                                   0.2       7.1                                                    2.5 hours                                                          Catalyst D 50 vol. % NO +                                                                             0.2       39.1                                                   2 vol. % Cl.sub.2                                                             at 400° F. for                                                         2.5 hours                                                          ______________________________________                                    

These data show that under essentially identical treatment conditionsemploying essentially identical catalysts, nitric oxide, and especiallynitric oxide in admixture with chlorine, resulted in significantlygreater BHA levels than nitrogen dioxide.

EXAMPLE 4

A Pd Al₂ O₃ catalyst had a fresh BHA activity of 57.1 mole/mole/Pd/hr.When deactivated in an atmosphere of 80% hydrogen and 20% steam at 800°F. for 1 hr. the BHA activity diminished to zero. Treatment with oxygenat 1100° F. for 2.5 hr increased the activity to 14.6 mole/mole Pd/hr.However, treatment with NO at 390° F. for 2.5 hr followed by heliumpurge restored the BHA activity to 23.5 mole/mold Pd/hr.

EXAMPLE 5

Zirconium was introduced as a complex cation with aluminumhydroxychloride during the zeolite/alumina mulling step of the catalystpreparation. This component was added in order to improve the dispersionof palladium and to increase the physical strength of the catalyst. Thecatalyst contained 2.5 wt. % ZrO₂, which replaced 7 wt. % of the aluminabinder of a 65 wt. % ZSM-5/35 wt. % Al₂ O₃ formulation. For comparison,a catalyst with 65% ZSM-5 in 35% Al₂ O₃ matrix was also prepared. Bothcatalysts contained 0.39% palladium. BHA levels of fresh, steamdeactivated, and NO rejuvenated catalyst are shown in the followingtable.

                  TABLE 6                                                         ______________________________________                                        Benzene Hydrogenation Activity                                                (NO Treatment at 390° F. for 2.5 hr.)                                                Al.sub.2 O.sub.3 Support                                                                  Al.sub.2 O.sub.3 /ZrO.sub.2 Support                 Pretreatment  BHA         BHA                                                 ______________________________________                                        Fresh         20.4        23.8                                                Reduced                                                                       (H.sub.2, 800° F., 1 hr)                                                             4.1         8.7                                                 NO treated    40.5        36.3                                                Steamed                                                                       (80% H.sub.2 /20% steam,                                                                    2.4         5.9                                                 800° F., 1 hr)                                                         NO treated    19.6        19.1                                                ______________________________________                                    

On hydrogen-reduced or hydrogen/steam deactivated catalysts, higher BHAactivity was observed when zirconium was present. In both cases, thedeactivated catalysts could be rejuvenated with nitric oxide after whichthe hydrogenation activity increased to at least that of the freshcatalyst.

EXAMPLE 6

A variety of zeolite-supported platinum catalysts were prepared andtreated under the conditions and with the observed BHA levels(mole/mole/ Pt/hr) shown in the following table.

                  TABLE 7                                                         ______________________________________                                        BHA Levels (at 212° F.) Of Pt Zeolite                                  Catalyst Compositions                                                         Catalyst     Treatment           BHA                                          ______________________________________                                        0.66 wt. %   Fresh Cat.          969                                          Pt/Zeolite Beta/                                                              Alumina                                                                       0.66 wt. %   80 vol. % Air/20 vol. % H.sub.2 O                                                                 580                                          Pt/Zeolite Beta/                                                                           at 1000° F., 3 hr.                                        Alumina                                                                       0.66 wt. %   50 vol. % NO/2 vol. % Cl.sub.2                                                                    2160                                         Pt/Zeolite Beta/                                                                           at 570° F., 3 hr.                                         Alumina                                                                       0.66 wt. %   50 vol. % NO/2 vol. % Cl.sub.2                                                                    1400                                         Pt/Zeolite Beta/                                                                           at 570° F., 3 hr.                                         Alumina                                                                       0.66 wt. %   2 vol. % Cl.sub.2 in 98 vol. % N.sub.2                                                            716                                          Pt/Zeolite Beta/                                                                           at 570° F., 3 hr.                                         Alumina                                                                       0.6 wt. %    Fresh Cat.          226                                          Pt/Alumina                                                                    0.6 wt. %    80 vol. % Air/20 vol. % H.sub.2 O                                                                  9                                           Pt/Alumina   at 570° F., 3 hr.                                         0.6 wt. %    50 vol. % NO/2 vol. % Cl.sub.2                                                                    657                                          Pt/Alumina   at 570° F., 3 hr.                                         0.66 wt. %   Fresh Cat.          969                                          Pt/Zeolite Beta/                                                              Alumina                                                                       0.66 wt. %   H.sub.2, 750° F., 1 hr.                                                                    223                                          Pt/Zeolite Beta/                                                                           65 vol. % Air/35 vol. % H.sub.2 O                                Alumina      at 1000° F., 18 hr.                                       0.66 wt. %   50 vol. % NO/2 vol. % Cl.sub.2                                                                    945                                          Pt/Zeolite Beta/                                                                           at 570° F., 3 hr.                                         Alumina                                                                       1.1 wt. %    Fresh Cat.           81                                          Pt/ZSM-5/Alumina                                                              1.1 wt. %    H.sub.2, 750° F., 1 hr.                                                                     43                                          Pt/ZSM-5/Alumina                                                                           65 vol. % Air/35 vol. % H.sub.2 O                                             1000° F., 18 hr.                                          1.1 wt. %    50 vol. % NO/2 vol. % Cl.sub.2                                                                    242                                          Pt/ZSM-5/Alumina                                                                           at 570° F., 3 hr.                                         0.1 wt. % Pt/                                                                              Fresh Cat.          148                                          ZSM-5/Alumina                                                                 0.1 wt. % Pt/                                                                              50 vol. % NO/2 vol. % Cl.sub.2                                                                    181                                          ZSM-5/Alumina                                                                 0.1 wt. % Pt/                                                                              50 vol. % NO/2 vol. % Cl.sub.2                                                                    206                                          ZSM-5/Alumina                                                                 ______________________________________                                    

What is claimed is:
 1. A process for dispersing or redispersing a GroupVIII noble metal component of a catalytic material comprising the noblemetal component supported on a porous inorganic support materialcontaining no, or at most a minor, amount of carbonaceous material whichprocess comprises:(a) contacting the supported Group VIII noble metalcomponent on the support with nitric oxide at a temperature of 200° to1000° F. providing dispersion or redispersion of the noble metalcomponent on the support; and, (b) purging nitrogen oxide(s) at atemperature of 200° to 1000° F. from the catalytic material comprising adispersed/redispersed noble metal component, the benzene hydrogenationactivity of the catalytic material containing the supporteddispersed/redispersed noble metal being substantially higher than thebenzene hydrogenation activity of the catalytic material prior tocontacting step (a).
 2. The process of claim 1 wherein there is at leasta 20% increase in the benzene hydrogenation activity of the supporteddispersed/redispersed noble metal species following contacting step (b)compared to the benzene hydrogenation activity of the supported noblemetal species prior to contacting step (a).
 3. The process of claim 1wherein the noble metal species is at least one metal, oxide or sulfideselected from the group consisting of platinum, palladium, iridium,osmium, rhodium and ruthenium.
 4. The process of claim 3 wherein thereis additionally present at least one non-noble metal selected from GroupIB, Group IIIB, Group IVB, Group VB, Group VIB, Group VIIB or Group VIIIof the Periodic Table of the Elements as a promoter.
 5. The process ofclaim 1 wherein the porous inorganic support is a siliceous material. 6.The process of claim 1 wherein the porous inorganic support is acrystalline material.
 7. The process of claim 1 wherein the porousinorganic support is a zeolite.
 8. The process of claim 7 wherein thezeolite is at least one member of the group consisting of zeolite, L, X,Y, Beta, ZSM-5, ZSM-11, ZSM-12, ZSM-20, ZSM-23, ZSM-35, ZSM-38 andZSM-48.
 9. The process of claim 1 wherein prior to contacting step (a),the average crystallite size of the noble metal component is at leastabout 25 Angstroms.
 10. The process of claim 1 wherein prior tocontacting step (a), the average crystallite size of the noble metalcomponent is as least about 50 Angstroms.
 11. The process of claim 1wherein prior to contacting step (a), the average crystallite size ofthe noble metal component is at least about 100 Angstroms.
 12. Theprocess of claim 1 wherein purging is carried out with inert gas.
 13. Aprocess for dispersing or redispersing a Group VIII noble metalcomponent of a catalytic material comprising the Group VIII noble metalcomponent on a porous inorganic support material which comprisescontacting the supported Group VIII noble metal component with a gaseousmixture comprising a major amount of nitric oxide and a minor amount ofgaseous halogen at a temperature of 200° to 1000° F. providingdispersion or redispersion of the noble metal component on the support,and purging nitric oxide from the treated catalytic material at atemperature from 200° to 1000° F., the benzene hydrogenation activity ofthe catalytic material containing the supported dispersed/redispersednoble metal component being substantially higher than the benzenehydrogenation activity of the catalytic material prior to contact withthe gaseous mixture.
 14. The process of claim 13, wherein there is atleast a 20% increase in the benzene hydrogenation activity of thesupported dispersed/redispersed noble metal species following contactingwith nitric oxide compared to the benzene hydrogenation activity of thesupported noble metal species prior to contacting with nitric oxide. 15.The process of claim 13, wherein the noble metal component is as leastone metal, oxide or sulfide selected from the group consisting ofplatinum, palladium, iridium, osmium, rhodium and ruthenium.
 16. Theprocess of claim 15 wherein there is additionally present at least onenon-noble metal selected from Group IB, Group IIIB, Group IVB, Group VB,Group VIB, Group VIIB or Group VIII of the Periodic Table of theElements as a promoter.
 17. The process of claim 13 wherein the porousinorganic support is a siliceous material.
 18. The process of claim 13wherein the porous inorganic support is a crystalline material.
 19. Theprocess of claim 13 wherein the porous inorganic support is a zeolite.20. The process of claim 19, wherein the zeolite is at least one memberof the group consisting of zeolite, L, X, Y, Beta, ZSM5, ZSM-11, ZSM-12,ZSM-20, ZSM-23, ZSM-35, ZSM-38 and ZSM-48.
 21. The process of claim 13wherein prior to contacting with nitric oxide, the average crystallitesize of the noble metal component is at least about 25 Angstroms. 22.The process of claim 13 wherein prior to contacting with nitric oxide,the average crystallite size of the noble metal component is at leastabout 50 Angstroms.
 23. The process of claim 13 wherein prior tocontacting with nitric oxide, the average crystallite size of the noblemetal component is at least about 100 Angstroms.
 24. The process ofclaim 17 wherein the siliceous material is a zeolite and the source ofgaseous halogen is chlorine.
 25. The process of claim 13 wherein theconcentration of nitric oxide is at least about 0.1 volume percent. 26.The process of claim 13 wherein the concentration of gaseous source ofhalogen is at least about 0.01 volume percent.